In central vacuum systems there are two main types of components, namely built in components and portable components. The built in components consist of the central vacuum motor which is typically installed in a basement or garage of a dwelling, and plastic conduits which run under floors and inside walls and are connected to the vacuum motor. The conduits are typically provided with wall mounted inlet valves. The portable components typically comprise a hose, having a wand at the end, which in turn has a head. Passive and active heads are used with active heads such as beater bars being more popular for carpeted surfaces.
In such central vacuum systems the portable components are connected to the built in components at fittings commonly referred to as inlet valves. The valves are usually mounted in walls and are provided with a hinged cover which seals a vacuum opening. A hose cuff is provided on the hose which mates with and seals with the vacuum opening in the valve, which becomes exposed when the hinged cover is lifted.
Most usually the valve is comprised of a number of different elements which are attached together to form an assembly. In the past there have been many different types of inlet valve assemblies for the purpose of providing a convenient hose attachment for central vacuum systems. Such assemblies usually comprise a backing or mounting plate, which is attached to a wall stud or the like and a cover plate or valve which is inserted into the backing or mounting plate and which carries the hinged cover for the vacuum opening. The vacuum conduit is usually attached to the back of the backing plate and wires may be run along side the conduit to pass through the backing plate and to connect to switches or contacts for engaging the vacuum motor. Thus when the hose cuff of the portable hose is inserted into the vacuum opening, a low voltage circuit is closed and the vacuum motor is engaged. An example of this type of fitting is shown in U.S. Pat. No. 4,336,427 to Lindsay.
Typically, a rubber seal or gasket is provided between the cover plate and the backing plate to ensure a good vacuum tight seal. When the rubber gasket or seal is mounted inside of the vacuum opening in the backing plate, it becomes partially exposed and thus is susceptible to damage during installation of the drywall over or around the fitting. Typically in new house installations, the backing plate will be mounted onto the end of the conduit and then nailed to an adjacent stud. For backing plates having a perimeter wall, it has been discovered that it is common for the drywall installer to use a router to define an opening in over mounted drywall. As the router is passed across the face of the backing plate, it may have a tendency to slip into the vacuum opening in the backing plate and damage the rubber seal or gasket. A damaged seal results in a loss of suction which can impair the effectiveness of the central vacuum cleaning system. Additionally, there is a risk that blocking debris may become lodged in the vacuum tube, since the pipe opening is fully exposed during this operation.